Outer membrane phospholipase A1 (OMPLA) is an

acyl In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an alkyl group (). In organic chemistry, the acyl group (IUPAC n ...

hydrolase Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...

with a broad substrate specificity (EC:3.1.1.32.) from the bacterial outer membrane. It has been proposed that Ser164 is the active site of the protein (

UniProt UniProt is a freely accessible database of protein sequence and functional information, many entries being derived from genome sequencing projects. It contains a large amount of information about the biological function of proteins derived from ...

) This integral membrane

phospholipase A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca2+, an essential step in ...

was found in many

Gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

and has a broad substrate specificity . The role of OMPLA has been most thoroughly studied in

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

, where it participates in the secretion of

bacteriocin Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally, and ec ...

s. Bacteriocin release is triggered by a lysis protein (bacteriocin release protein or BRP), followed by a phospholipase dependent accumulation of lysophospholipids and free fatty acids in the outer membrane. The reaction products enhance the permeability of the outer membrane, which allows the semispecific secretion of bacteriocins. One speculative function of OMPLA is related to organic solvent tolerance in bacteria. Structurally, it consists of a 12-stranded antiparallel

beta-barrel In protein structures, a beta barrel is a beta sheet composed of tandem repeats that twists and coils to form a closed toroidal structure in which the first strand is bonded to the last strand (hydrogen bond). Beta-strands in many beta-barrels are ...

with a convex and a flat side. The active site residues are exposed on the exterior of the flat face of the beta-barrel. The activity of the enzyme is regulated by reversible dimerisation. Dimer interactions occur exclusively in the membrane-embedded parts of the flat side of the beta-barrel, with polar residues embedded in an apolar environment forming the key interactions. The active site His and Ser residues are located at the exterior of the beta-barrel, at the outer leaflet side of the membrane. This location indicates that under normal conditions the substrate and the active site are physically separated, since in E. coli phospholipids are exclusively located in the inner leaflet of the outer membrane.

References

Protein domains Outer membrane proteins {{hydrolase-stub